An epoxy resin is utilized in wide application fields such as coating material, insulating material for electric and electronics parts, and adhesives, because the hardened material has an excellent performance in terms of mechanical characteristics, electrical characteristics, thermal characteristics, chemical resistance, and adhesion properties. An epoxy resin composition generally used at present is a so-called two component type one, wherein two fluids, an epoxy resin and a hardener, are mixed just before use.
A two component epoxy resin composition, although which can be hardened at room temperature, requires for an epoxy resin and a harder to separately be stored, and to be used after weighing and mixing both when needed, which makes storage or handling cumbersome and complicated.
In addition, because of limited usable life, a large quantity of mixing in advance is not allowed, and formulating frequency is increased, which makes decrease in efficiency unpreventable.
To solve the problems of such a two component epoxy resin formulation, there have been some proposals of one component epoxy resin compositions. For example, those wherein an epoxy resin is formulated with a latent hardener such as dicyandiamide, a BF3-amine complex, an amine salt or a modified imidazole compound, and the like are included.
However, among these latent hardeners, those excellent in storage stability have lower hardening property and require high temperature or a long period of time for hardening, while those having high hardening property have low storage stability and therefore require to be stored at low temperature, for example, at −20° C. For example, dicyandiamide provides a storage stability of a formulated product of not shorter than 6 months at room temperature, however, requires a hardening temperature of not lower than 170° C., and in the case of combined use of a hardening accelerator to lower this hardening temperature, hardening at, for example, 130° C. becomes possible but on the other hand storage stability at room temperature becomes insufficient, which inevitably requires storage at low temperature. Therefore, a composition satisfying both high hardening property and excellent storage stability has strongly been required. In addition, in the case of obtaining a film-like molded product or a product of a substrate impregnated with an epoxy resin, a formulated product containing a solvent or a reactive diluent and the like is observed in many cases, and use of a conventional latent hardener as a hardener for such a formulated product significantly decreases storage stability and substantially requires to make a two component type hardener, and therefore improvement of such inconvenience has been required.
In response to such requirement, many researches have been made, for example, in Patent Document 1, a hardener for an epoxy resin coated at the surface with a reaction product of an isocyanate compound is described.
However, recently, in particular in an electronics device field, further improvement of hardening property without impairing storage stability has strongly been required for a one component epoxy resin composition used as one of connection materials, to respond to higher density or improvement of connection reliability of a circuit, or to use low heat resistant material as means for weight reduction of mobile device, or aiming at significant improvement of productivity, which has been difficult to attain by conventional technology.                [Patent Document 1] JP-A-1-70523        